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Discussion Starter #1
Hello everyone, I'm new to the forum, but I have been reasearching and reading threads on here about finding oil or what looks like oil in the coolant tank religiously for the last week. Unfortunately none of the threads have helped my current situation and I was wondering if anyone had any input. I recently bought a used 2004.5 GMC sierra mason dump with 164k miles on the odometer. After driving it for several days I noticed what looked like oil in the coolant tank. I took it to my local diesel mechanic and was told it was most likely my oil cooler. Proceeded to do my own research and found it was more likely to be a head gasket issue. There is no pressurization of the over flow tank when the truck is cool and the upper radiator hose is soft. I proceeded to buy and install a brand new oem oil cooler myself. I also installed new thermostats changed the oil and installed a new coolant tank cap ( I thought maybe the seal was bad and was preventing the tell tale pressurization of a bad head gasket) and finally new dexcool coolant. A day later after driving the truck i built up a thin layer of black substance on top of the coolant again in my tank. Doesnt look like im using any coolant and the truck has been steady at 185-190 degrees when cruising. My next step is a block tester but before I do that has anyone had a similar scenario? I appreciate any input.

Thanks!
 

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Did you flush the coolant or just drain it out? It will probably take a few flushes to get any oil out of the system.
 

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Discussion Starter #4
Most of it drained out of the oil cooler when it came off the block, the rest drained from the petcock. I didn't flush it, I've had my hopes up that it is just left over residue. You're definitely right in that i should flush it several times. Still getting no pressurization/ I check at the start of every day.
 
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